An anisotropically conductive sheet is a sheet exhibiting conductivity only in its thickness-wise direction or having pressure-sensitive conductive conductor parts exhibiting conductivity only in the thickness-wise direction when they are pressed in the thickness-wise direction. Since such an anisotropically conductive sheet has such features that compact electrical connection can be achieved without using any means such as soldering or mechanical fitting, and that soft connection becomes feasible with mechanical shock or strain absorbed therein, it is widely used as an anisotropically conductive connector for achieving electrical connection between circuit devices, for example, electrical connection between a printed circuit board and a leadless chip carrier, liquid crystal panel or the like, in fields of, for example, electronic computers, electronic digital clocks, electronic cameras and computer key boards.
In electrical inspection of circuit devices such as printed circuit boards and semiconductor integrated circuits, it is conducted to interpose an anisotropically conductive elastomer sheet as a connector between an electrode region of a circuit device, which is an object of inspection, and an inspection electrode region of a circuit board for inspection for the purpose of achieving electrical connection between electrodes to be inspected formed on one surface of the circuit device and inspection electrodes formed on the surface of the circuit board for inspection.
As such anisotropically conductive sheets, there have heretofore been known those of various structures, such as those obtained by uniformly dispersing metal particles in an elastomer (see, for example, Patent Art. 1), those obtained by unevenly dispersing a conductive magnetic metal in an elastomer, thereby forming a great number of conductive path-forming parts each extending in a thickness-wise direction thereof and an insulating part for mutually insulating them (see, for example, Patent Art. 2) and those obtained by defining a difference in level between the surface of each conductive path-forming part and the insulating part (see, for example, Patent Art. 3).
In these anisotropically conductive sheets, conductive particles are contained in an insulating elastic polymeric substance in a state oriented so as to align in the thickness-wise direction, and each conductive path is formed by a chain of a great number of conductive particles.
Such an anisotropically conductive sheet can be produced by, for example, charging a molding material with conductive particles exhibiting magnetism contained in a polymeric substance-forming material, which will become an elastic polymeric substance by being cured, into a molding cavity of a mold to form a molding material layer, and applying a magnetic field to the molding material layer and curing treatment.
However, the use of a conventional anisotropically conductive sheet as a connector in electrical inspection of a circuit device having projected electrodes composed of, for example, a solder involves the following problems.
Namely, when an operation that projected electrodes that are electrodes to be inspected of a circuit device, which is an object of inspection, are brought into contact under pressure with the surface of the anisotropically conductive sheet is conducted repeatedly, permanent deformation by the pressure contact of the projected electrodes, and deformation by abrasion occur on the surface of the anisotropically conductive sheet, and so the electric resistance values of the conductive path-forming parts in the anisotropically conductive sheet are increased, and the electric resistance values of the respective conductive path-forming parts vary, thereby causing a problem that the following inspection of circuit devices becomes difficult.
In addition, particles with a coating layer composed of gold formed thereon are generally used as conductive particles for forming the conductive path-forming parts for the purpose of achieving good conductivity. However, an electrode material (solder) forming electrodes to be inspected in circuit devices migrates to the coating layers on the conductive particles in the anisotropically conductive sheet when electrical inspection of a great number of circuit devices is conducted continuously, whereby the coating layers are modified. As a result, a problem that the conductivity of the conductive path-forming parts is lowered arises.
Further, the use of a conventional anisotropically conductive sheet as a connector in electrical inspection of a circuit device having pad electrodes composed of, for example, aluminum involves the following problems.
Namely, in the circuit device having the pad electrodes, a resist film having a thickness greater than the thickness of each pad electrode is generally formed on the surface of the circuit device. In order to be surely and electrically connected to the pad electrodes of the circuit device, on which such a resist film has been formed, an anisotropically conductive sheet, in which conductive path-forming parts projecting from the surface of an insulating part have been formed, is used. However, when such an anisotropically conductive sheet is used repeatedly, permanent compression deformation occurs on the conductive path-forming parts, so that the electric resistance values of the conductive path-forming parts in the anisotropically conductive sheet are increased, or stable electrical connection of the conductive path-forming parts to the pad electrodes is not achieved. As a result, the electric resistance values between the pad electrodes that are electrodes to be inspected and inspection electrodes in a circuit board for inspection vary, thereby causing a problem that the following inspection of circuit devices becomes difficult.
In order to solve the above-described problems, it is conducted in inspection of a circuit device to fabricate an anisotropically conductive connector device by an anisotropically conductive sheet and a sheet-like connector obtained by arranging a plurality of electrode structures each extending through in a thickness-wise direction of a flexible insulating sheet composed of a resin material in the insulating sheet and bring electrodes to be inspected into contact under pressure with the electrode structures of the sheet-like connector in this anisotropically conductive connector device, thereby achieving electrical connection with the circuit device that is an object of inspection (see, for example, Patent Art. 4).
The sheet-like connector in such an anisotropically conductive connector device is generally produced in the following manner.
As illustrated in FIG. 24(a), a laminate material 90A obtained by forming a metal layer 92 on one surface of an insulating sheet 91 is first provided, and through-holes 98H each extending through in a thickness-wise direction of the insulating sheet 91 are formed in the insulating sheet 91 by laser beam machining, dry etching or the like as illustrated in FIG. 24(b).
As illustrated in FIG. 24(c), a resist film 93 is then formed on the metal layer 92 on the insulating sheet 91, and for example, an electroplating treatment is conducted by using the metal layer 92 as a common electrode, whereby a metal deposit is filled into each of the through-holes 98H in the insulating sheet 91 to form a short circuit part 98 integrally linked to the metal layer 92, and at the same time, form a projected front-surface electrode part 96 integrally linked to the short circuit part 98 on the front surface of the insulating sheet 91.
Thereafter, the resist film 93 is removed from the metal layer 92, and as illustrated in FIG. 24(d), a resist film 94A is formed on the front surface of the insulating sheet 91 including the front-surface electrode parts 96, and moreover resist film portions 94B are formed on the metal layer 92 in accordance with a pattern corresponding to a pattern of back-surface electrode parts to be formed. The metal layer 92 is subjected to an etching treatment to remove exposed portions of the metal layer 92, thereby forming back-surface electrode parts 97 as illustrated in FIG. 24(e), thus resulting in the formation of the electrode structures 95 to obtain the sheet-like connector 90.
However, the above-described anisotropically conductive connector device involves the following problem.
Since it is difficult in fact to supply a current even in current density distribution to the overall surface of the metal layer 92 in the electroplating treatment step of forming the short circuit parts 98 and front-surface electrode parts 96 in the production process of the sheet-like connector 90, the growing rate of the plating layer varies with individual through-holes 98H in the insulating sheet 91 due to the unevenness of the current density distribution, so that a scatter occurs on the projected height of the front-surface electrode parts 96 formed as illustrated in FIG. 25(a). Upon conducting electrical connection of the sheet-like connector 90 to a circuit device 6, the scatter of projected height in the front-surface electrode parts 96 is absorbed by the flexibility that the insulating sheet 91 has as illustrated in FIG. 25(b). In other words, the insulating sheet 91 is distorted according to the degree of scatter of the projected height in the front-surface electrode parts 96, whereby the electrode structures 95 are displaced, so that each of the front-surface electrode parts 96 comes into contact with each of electrodes 7 to be inspected, thereby achieving necessary electrical connection.
However, when the arrangement pitch of the electrodes 7 to be inspected in the circuit device 6 is small, i.e., the arrangement pitch of the electrode structures 95 in the sheet-like connector 90 is small, a ratio of a clearance between electrode structures 95 adjoining each other to the thickness of the insulating sheet 91 becomes small, so that the flexibility of the whole sheet-like connector 90 is greatly lowered. As a result, the scatter of projected height in the front-surface electrode parts 96 is not sufficiently absorbed upon conducting electrical connection of the sheet-like connector 90 to the circuit device 6 as illustrated in FIG. 25(c). In other words, the electrode structures 95 are not sufficiently displaced, so that, for example, a front-surface electrode part 96 (in the drawing, a left-side front-surface electrode part 96) smaller in projected height comes into no contact with the electrode 7 to be inspected, and so it is difficult to achieve stable electrical connection to the electrode 7 to be inspected.    Patent Art. 1: Japanese Patent Application Laid-Open No. 93393/1976;    Patent Art. 2: Japanese Patent Application Laid-Open No. 147772/1978;    Patent Art. 3: Japanese Patent Application Laid-Open No. 250906/1986;    Patent Art. 4: Japanese Patent Application Laid-Open No. 231019/1995.